Safety circuits for thermionic apparatus



May 5, 1942. E. G. GAGE SAFETY CIRCUITS FOR THERMIONIC APPARATUS 2Sheets-Sheet 1 Filed May 29, 1340 .INVENTOR. {ow/mo 6.61465 BY A TTOR/V5 X May 5, 1942. E. G. GAGE 2,281,571

SAFETY CIRCUITS FOR THERMIONIC APPARATUS FilGd May 29, 1940 2Sheets-Sheet 2 ERIE INVENTOR. Eon/5R0 6. 6A6

ATTORNEY Patented May 5, 1942 SAFETY CIRCUITS FOR THERMIONIC APPARATUSEdward G. Gage, Brooklyn, N. Y., assignor, by direct and mesneassignments, of two-thirds to Leon Ottinger, New York, N. Y.

Application May 29, 1940, SerialNo. 337,806

4 Claims.

Ina co-pending application Serial No. 281,511,

I have disclosed a system wherein the total voltage of a dangerouscircuit is divided by means of resistance inserted in series betweensections of a source of high potential such as a battery. By interposinga resistance between any two sections of the battery likely to becontacted, and the body, it is impossible to effect contact with anysection Without at the same time including a resistance suflicient tolimit the current to a safe value.

The present invention contemplates dividing both the current and thevoltage in a dangerous voltage circuit, for example, current and voltagesuch as may be derived from a transformer or filter condenser,respectively, andfeeding, for example, the plates of thermionic means,more especially as a tube including a plurality of anodes or as aplurality of tubes with individual plates.

An object of the invention is to provide in a circuit of the aforesaidnature a plurality of parallel paths for direct or alternating currentflow, the total current or sum of the currents in all paths beingdangerous, but the current in any single path being of a safe value.

Another object of the invention is to provide a filter condenser whichis safe to handle and yet possesses high capacity and is charged to adangerous voltage.

Still another object ofthe invention is to, combine in a single unit afilter condenser, carrying a dangerous current and voltage, with asmoothing impedance.

The invention has for an object, also, to provide a novel constructionof transformer capable of supplying a dangerous voltage but safe tohandle.

In carrying out the invention, the circuit is so designed that thecurrent paths, for example to a thermionic transmitter tube, aremaintained separate by dividing the plate of the tube into separatedsections, each section being fed by a separate conductor, theoutputpaths being united as for radio frequency current flow by connectingeach plate section to a section of a condenser having one commonelectrode. Or, as an alternative, the plate sections may be connectedvto respective. primary coils of a transformer having a common outputsecondary. The filter condensers for the separate conductors, also, areof novel construction and embody coiled electrodes comprising conductingstrips and alternate sections of high resistance elements or wire. Asimilar construction of transformer is contemplated.

The nature of the invention, however, will best be understood whendescribed in connection with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of the safety circuits of a vacuum tubefor a radio frequency or audio frequenc amplifier operating at adangerous voltage and current.

Fig. 2 is a detail transverse section of a com bined safety filtercondenser and impedance carrying dangerous voltage.

Fig. 3 is a reduced plan view of a condenser electrode with intermediateresistance sections.

Fig. 4 is a transverse section illustrating a modification in thecondenser construction.

Fig. 5 is a schematic diagram illustrating a modified form of the novelsafety circuit.

Fig. 6 shows alternative means for providing a safety transformer fordividing the output circuit into parallel paths by means of resistanceslocated inside a casing, and an oscillator circuit connected thereto.

Fig. 7 is a detail transverse section of a safety transformer carrying adangerous voltage and embodyingconductors of relatively high and lowresistance connected in series.

Referring to the drawings, more particularly to Fig, 1, l0 designates asource of current voltage, for example alternating, which may, forconvenience, have a frequency-of sixty cycles, and is connected to theprimary winding II of a multiple section transformer, of which I2 is thecore.

Separate transformer secondary sections l3, I4, I5, and I6 are providedon the core, each delivering the same and a relatively high voltage; anda further transformer Il delivers a low volt age to the filament I8 of ahigh impedance transmission vacuum tube I9 of the three-element typehaving the grid 20. Voltage from the secondary sections I3, I4, I5, andI6 is delivered to the plate of said transmitter tube which, inaccordance with the invention, is divided into a like number of sections2I, 22, 23, and 24 connected respectively to the said transformersections through leads 25, 26, 21, and 28, respectively, and seriesinductances 2I', 22, 23, and 24'. There is afforded thereby parallelpaths each at substantially thesame voltage and a safe current flow, saynot in. excess, of 10 milliamperes. Respective filter condensers 30, 3|,32, and 33, preferably of the novel construction hereinafter set forth,are included in the different leads.

The outputs from the tube plates or anodes are connected to respectiveparallel connected condensers 34, 35, 36, and 31 for uniting the highfrequency outputs of the plate circuits as through adouble-throw'double-pole switch 38 to one terminal of a tank tuningcondenser 39. There is associated therewith, also, an oscillator coil 40for coupling the radio frequency circuit to the antenna M and ground.42, the grid being grounded at the same time through the coil 43coupled to an input coil 44. By throwing switch 38 in the oppositedirection, the condensers may be connected to operate a sound reproducerthe grid then being grounded through a coil 43 coupled to the audiofrequency input coil 44.

As shown in Figs. 2 and 3, the filter condensers comprise a laminatediron core 45 which is surrounded'by'coiled condenser electrodes, each ofwhich may consist of narrow strips of metal foil 46, 41, and 48, and 49,50, and 5|, respectively, with alternate conductors 46, 41' and 49, 50connected between. These conductors may be of high resistance wire suchas Nichrome; or, with lower power condensers, ordinary fine copper wiremay provide the required resistance. Dielectrics 52 and 52' which may beof insulating paper are wound between the condenser electrodes withresistance wire in series. The combined filter condenser and impedanceshown constitutes, in effect, a plurality of impedances in series withcondensers in shunt between each impedance, as in the standard filternetwork. The

advantage of such construction lies in the fact that the entire networkis combined in a single unit with but four exposed terminals 53, 53, 54,and 54', one of which, preferably the outside foil terminal 53, may begrounded.

As all conductors as well as the foil portions are rolled up in acompact roll, it is not possible to contact any portion accidentallywithout including resistance in series with ones body sufficient tolimit the condenser discharge, as determined by the capacity of thecondenser, to a safe value.

The condenser capacity plays an important part in the safety feature ofthe device. Because the filter network is divided up into sections, aseparate section being used for each plate section of the vacuum tube,the capacity of each condenser-impedance unit is only a fraction of thetotal capacity required for current smoothing, in

the case cited being but one-fourth of such capacity as there are fourplate sections. This means that the voltage and current through the bodyfrom accidental contact with any one section is reduced to one-fourth ofwhat it would be if the capacity were combined in a single condenser.

Instead of using high-resistance wire to provide inductance andresistance between condensers, small carbon resistors in the form ofshort fiat strips 55 or rods, Fig. 4, may be used in between theelectrode portions 56, 51, and 58, and rolled with the condensers.

Each of the transformer sections I3, I 4, I5, and I6 are similarlyprovided with one or more intermediate protective resistances I3, I4,I5, and I6. Provision is also made, as by means of a high-voltagerectifier 60, for rectifying all currents passing from the commonterminal 6| of transformer sections I3, I4, I5, and I6, which isconnected to one terminal of the'rectifler, the

other being grounded at 62. The filament I8 of the vacuum tube I8 isalso grounded as at 64.

In Fig. 5 a similar circuit is disclosed but the tube anodes 10, 1|, 12,and 13 are connected respectively to primary coil 14, 15, 1G, and 11coupled to a common secondary 1 8 for the antenna 19, grid of the tubebeing grounded through the input system 8|. The coils are wound withrespect to the secondary such that their effects thereon are additiveand preferably are tuned alike.

Fig. 6 illustrates an oscillator type of circuit wherein, also, thesafeguarding resistances of the transformer are arranged in a differentmanner in the dividing of the electrical energy into a plurality ofpaths. Thus, the one lead of transformer secondary 86 is divided intofour branches 81, 88, 89, and 90 which have safeguarding seriesresistances 9|, 92,93, and 94, all, together with the transformer as awhole, being encased in a suitable housing from which extend the leads96, 91, 98, and 99 to the anodes I00, IOI, I02, and I03, respectively.

A convenient arrangement for interposing the secondary resistances in atransformer is illustrated in Fig. 7 of the drawings. As indicatedtherein, a primary winding I05 is coiled about a central core I06 oflaminated iron and about this is wound in the required number ofconvolutions, together with an intermediate layer of insulation I01, thesecondary wire winding I08 having interposed at different portions alongits length safeguarding resistors I09, H0, III, H2, H3, and I I4. Oneterminal H5 of such secondary may be grounded as at H6, and to the otherterminal H1 a lead H8 connects to the desired means to be operated.Difierent secondary sections similar to that hereinbefore described maybe mounted adjacently along the core I06 to provide the desired numberof paths for the energy to be supplied.

In the practical application of the invention, the thermionic tubesupplied with the energy through the plurality of paths shouldpreferably be one of high impedance, designed for upwards of 10,000volts plate voltage. This is to reduce the plate current to as low aninitial value as possible.

Assuming the total plate current to be forty milliamperes, a dangerouscurrent, then it will be seen that by dividing up the plate intosections in parallel, each section will carry but 10 milliamperes, whichis a safe current. If desired, the plate may be divided into more thanthe number shown, thus further decreasing the current in each individualsection; or, by maintaining the current of each section of the samevalue, more power may be drawn from the tube with more sections. Thesame general rule holds good for the transformer secondary sections andthe filter condenser with combined impedance, as well as the alternativesystems shown in Figs. 5 and 6 of the drawings.

Assuming that each plate section carries I0 milliamperes, it would benecessary for a person to contact all four sections and the ground inorder to receive the full current of 40 milliameres. As this would beconsiderable ofa feat,

it would not be done accidentally, particularly as the different currentpaths are to be separated as far as practicable.

Contacting but one section and the ground, which would be the ordinaryaccidental contact, would pass not in excess of 10 milliamperes throughthe body.'

Contacting the radio frequency path from the plate, i. e. the portionoutside of the condenser electrodes 34, 35, 36, and 31, Fig. l, whichcomprises the oscillating circuit of the tube, is without danger as thecurrent is of radio frequency.

The maximum low frequency or direct current that may be obtained fromthe divided supply circuits shown in Fig. 1 would be determined by thelowest resistance which might be interposed between the points ofcontact of the body. If contact were made between ground and any one ofthe filter condenser output sections, then the lowest value would be thesum of the resistances in the transformer secondary section and theresistances in the filter condenser section.

It is important, therefore, that the lowest resistance possible to placebetween body and ground be such as to allow only a safe current to passat the maximum voltage.

Because the resistances in series with a secondary winding of thetransformer sections are wound up inside the secondary or suitablyencased, only the outside terminals can be contacted, and this alwaysincludes the enclosed resistances in series. The same is true of afilter condenser. Because the foil or outside terminals only can becontacted, it is not possible to contact these without including in thecircuit the resistances rolled up with the foil which are inside theroll and cannot be contacted.

As an example of safe values, the lowest resistance which should beallowed in circuit with 10,000 volts would be 1,000,000 ohms, whichwould pass milliamperes, a safe current. For such high voltage the humanbody may be considered practically a short-circuit. This resistanceshould be divided between copper loss and loss through concentratedresistance such as the Nichrorne wire winding or carbon resistorsinserted in series with the copper winding as in both a transformersecondary and the filter condenser impedance circuit. The problem thenbecomes a simple economic one. With no concentrated resistance inseries, the amount of copper wire, even of the smallest size, would haveto be enormous, several hundred pounds being necessary in a transformersection alone, for a 200-watt transmitter.

With all concentrated resistance in series, such as in the case of atransformer secondary and impedances wound entirely with Nichrome orsome such special resistance wire, as disclosed by me in a co-pendingapplication Serial #330,- 636, the power losses in a transmitter areconsiderable, while in a cathode ray device they are negligible.Therefore, a combination should be chosen for the highest generalefliciency. The actual total resistance of the plate circuit is, ofcourse, only a fraction of that of each separate plate section path, inthe present case one-fourth, since there are four sections.

I claim:

1. The combination with a source of electric current supply andunilateral means including a plurality of anodes operating at a combineddangerous voltage and current; of means, interposed between the saidsource of current supply and the said unilateral means, for separatingthe supply into a plurality of independent sources of dangerous voltageand corresponding paths to the respective anodes, each path includingresistance permanently located in series with the respective sources ofdangerous voltage such that all exposed parts of a path lie between asistance and the unilateral means, said resistance being of such highmagnitude that upon establishment of a closed circuit through saidexposed parts and the human body the current in the particular pathcontacted is reduced by said resistance therein to a safe value,together with means for recombining in an electrical work circuit thecurrents from the respective anodes.

2. The combination with a source of electric current supply andunilateral means including a plurality of anodes operating at a combineddangerous voltage and current; of means, interposed between the saidsource of current supply and the said unilateral means, for separatingthe supply into a plurality of independent sources of dangerous voltageand corresponding paths to the respective anodes, each path includingresistance permanently located in series with the respective sources ofdangerous voltage such that all exposed parts of a path lie between aresistance and the unilateral means, said resistance being of such highmagnitude that upon establishment of a closed circuit through saidexposed parts and the human body the current in the particular pathcontacted is reduced by said resistance therein to a safe value, andfilter condensers respectively connected in the circuits to said anodesand resistances permanently located in series therewith such that anyexposed parts of a condenser beyond a resistance when contacted by ahuman body affords a closed circuit having resistance of an order ofmagnitude, commensurate with the potential at the point of contact, tolimit to a safe value the current flow through the included portion ofthe condenser and the body, together with means for recombining in anelectrical work circuit the currents from the respective anodes.

3. The combination with a source of electric current supply andunilateral means including a plurality of anodes operating at a combineddangerous voltage and current; of means, interposed between the saidsource of current supply and the said unilateral means, for separatingthe supply into a plurality of independent sources of dangerous voltageand corresponding paths to the respective anodes, each path includingresistance permanently located in series with the respective sources ofdangerous voltage such that all exposed parts of a path lie between aresistance and the unilateral means, said resistance being of such highmagnitude that upon establishment of a closed circuit through saidexposed parts and the human body the current in the particular pathcontacted is reduced by said resistance therein to a safe value,together with electrical condensers each having an electrode connectedrespectively with the said anodes, and an electrical work circuitconnected to the combined other electrodes of said condensers.

4. The method of operating from an electrical source of dangerousvoltage and current electrical apparatus including unilateral meanshaving a plurality of anodes operative at a combined dangerous voltageand current, which comprises supplying energy from said source at adangerous voltage and dividing the total supplied energy into aplurality of independent paths corresponding to the number of anodes,restricting the current flow in each path for individually supplyingthereby each of said anodes with a safe current, and operating theelectrical apparatus from the said anodes by combining the effects ofthe output currents therefrom.

EDWARD G. GAGE.

